A027176 a(n) = A027170(2n-1, n-2).

7, 43, 185, 740, 2900, 11293, 43897, 170608, 663438, 2582058, 10058862, 39225116, 153111686, 598228961, 2339499161, 9157016216, 35870666366, 140623656686, 551684484386, 2165796506636, 8507878418516, 33441451138598, 131520611329070, 517527183621220, 2037464237218000

Offset

2,1

Links

Stefano Spezia, Table of n, a(n) for n = 2..1600

Formula

a(n) = 2*binomial(2*n+1, n-1) + binomial(2*n-1, n-2) - 4. - Christian Krause, May 10 2026

G.f.: (9 + 9/sqrt(1 - 4*x) - 8/(1 - x) + ((2*(sqrt(1 - 4*x) - 1) + x + 3*sqrt(1 - 4*x)*x + 4*x^3))/x^2)/2. - Stefano Spezia, May 11 2026

Crossrefs

Cf. A027170.

Sequence in context: A143569 A351936 A193697 * A383415 A244200 A334241

Adjacent sequences: A027173 A027174 A027175 * A027177 A027178 A027179

Keyword

nonn,easy

Author

Clark Kimberling

Extensions

a(24)-a(26) from Stefano Spezia, May 12 2026

Status

approved